NMR imaging of thermally polarized helium-3 gas

It is shown that thermally polarized He-3 gas can be used to measure important physical parameters and to design, test, and tune imaging sequences. The bulk values of T-1, T-2, and the diffusion coefficient were measured in a glass cell containing a mixture of helium-3 (0.8 bar) and oxygen (0.2 bar). They were found to be T-1 = 7 s, T-2 = 2.4 s, and D = 1.6 cm(2) s(-1). The relaxation times T-2* and T-1 and the apparent diffusion coefficient of thermally polarized helium-3 gas were measured in the rat lung, and these parameters were used to design a helium-3 optimized multi-spin-echo sequence which was shown to increase the signal-to-noise ratio sufficiently to obtain the first NMR-images of thermally polarized helium-3 in the rat lung, (C) 1999 Academic Press.